1. Field of the Invention
The present invention relates to a whether a hydrogen concentration in a gas is equal to or higher than a reference concentration, and also to an apparatus for detecting hydrogen.
2. Description of the Related Art
An apparatus for detecting hydrogen using a hydrogen absorbing alloy is disclosed in JP-A-10-73530. In the hydrogen detecting apparatus, a hydrogen absorbing alloy is fixed to one of the sides of a substrate, while a strain gauge is attached to another side thereof. In this structure, the stain gauge detects strain of the substrate caused by volume expansion of the hydrogen absorbing alloy in case of absorbing hydrogen. Concerning the hydrogen detecting apparatus using a hydrogen absorbing alloy, its selectivity with respect to hydrogen may be rather high, whereby the hydrogen detecting apparatus has an advantage in its high detection accuracy.
It is known that such a hydrogen absorbing alloy has P-T characteristics, where the hydrogen absorbing pressure might be uniquely determined in accordance with the operation temperature. Therefore, in a related art, a hydrogen detecting apparatus having the following manner has been developed. That is, an output of the strain gauge is monitored in a state where the operation temperature is always kept constant using a heater and the like. When a change occurs in the output of the stain gauge under said condition, the concentration of hydrogen is determined in that the detected gas reaches the concentration which corresponds to the hydrogen absorbing pressure according to the operation temperature as disclosed in JP-A-10-73530.
However, there is a drawback in such a hydrogen detecting apparatus, because keeping the condition of the constant temperature for the operation requires the continuous temperature control, and hence the heater must be energized for a long time period. In this regard, in case of the hydrogen concentration being monitored for a long term, the power consumption of the heater becomes very large, which ends up being costly. Moreover, the power supply source might be configured in relatively large size, which ends up increasing the manufacturing cost.
Especially, in the case of a hydrogen detecting apparatus which is disposed in a mobile unit, such as a fuel cell vehicle, which must be operated by the power supplied by a battery of which capacity is inevitably limited, and therefore, there is always the request to reduce power consumption. In this regard, it is disadvantageous for a fuel cell vehicle to increase the size of the battery.